356 SAMUEL H. SCUDDER ON THE 



doubt the precursor or ancestral type. Thus the Palaeoblattariae are more nearly allied in 

 the ground structure of their wings to certain neuropteroid Palaeodictyoptera of paleozoic 

 times than to the modern Blattariae ; and yet we can so completely trace in mesozoic 

 times the transition from the Palaeoblattariae to the Blattariae, that no reasonable doubt 

 can exist as to their descent, the one from the other. 



3. The ordinal distinction which is now found in the wing structure of modern insects 

 did not exist in paleozoic insects, but a common simple type of neuration which barely 

 admitted of family division. 



It will appear from this that, by a sort of principle of family continuity, we may recog- 

 nize in the paleozoic insects a tendency toward a differentiation in ordinal characters, suffi- 

 cient to enable us in an ex post facto fashion to distinguish between orthopteroid, neu- 

 ropteroid, etc. Palaeodictyoptera. 



In speaking above of the different orders of Heterometabola which were foreshadowed 

 in ancient times, I included the Coleoptera with a limitation, for the following reasons : 

 Troxites, the only supposed paleozoic beetle which has not been shown to be an arachnid, 

 is a very obscure object, and is very likely, as Brongniart has suggested, to be merely 

 some fruit. But there have been found wood borings of different kinds which so nearly 

 resemble similar excavations made now by Coleoptera that it is natural, though of course 

 not necessary, to attribute these to them. Yet if Coleoptera, with front wings differentiated 

 as those of to-day existed then, it would be rather anomalous, since all the paleozoic insects 

 we know excepting one, Phthanocoris, which foreshadowed the heteropterous Hemiptera, 

 had fore wings as completely membranous as the hind wings. 



It seems to me probable, therefore, though there are no further grounds for it than those 

 just given, coupled with the present relationship of the Coleoptera to other Heterometabola, 

 that Coleoptera sprang from such Palaeodictyoptera as were wood-borers throughout the 

 greater part of their life, and which at first showed no greater distinction between the 

 front and hind wings than existed generally in other Palaeodictyoptera ; but afterward those 

 races were preserved in which the thickening of the membrane of the upper wings the 

 better protected the insects while in their burrows for the marriage flight in open air. 

 Their habits would render their preservation in the rocks less frequent, and this special 

 differentiation would be likely to proceed rapidly, and to be retained even by those which 

 lost the wood boring habit; — a habit, by the way, likely to have existed with some insects 

 living in the vast carboniferous forests. 



Of the metamorphoses of the paleozoic insects we know absolutely nothing, for no lar- 

 val or pupal form has yet been found, nor even any apterous insect 1 which might by any 

 possibility be looked upon as such. The preparatory stages of existing Heterometabola ; 

 the fact that from every form of evidence the more " complete '' metamorphosis must 

 have been derived from the less complete; and the generally admitted proposition of 

 Brauer and others that metamorphosis, that is, radical change of form after birth, is a 

 secondary adaptive feature ; — these all lead us to conclude that the only significant change 

 in the paleozoic Palaeodictyopteron after leaving the egg was the acquirement of wings ; 

 and that the acquirement of wings was the lever which natural selection handled to 

 procure the present varied forms of metamorphosis in insects. 



1 Polyzosterites of Goldenberg is looked upon as a crustacean. 



